1. Field of the Invention
The invention relates to a support device for a camera dolly, comprised of four suspension supports each of which is disposed on the frame of the dolly at the respective corners of a rectangle and on each of which at least one ground wheel and at least one rail wheel are rotatably mounted so that the axes of the wheels are in planes parallel to the plane of the rectangle. Each support is rotatably releasably connected to a corresponding steering shaft extending perpendicularly to the plane of the rectangle, the connection being such that in a locked position rotation between the shaft and support cannot occur. Each support is also connected to a steering mechanism which serves to rotate the four steering shafts in rotationally synchronous fashion in the unlocked position.
2. Description of the Prior Art
A camera dolly equipped with a support wheel device of known type is operated by rolling it over the ground with the aid of ground wheels, or on rails. Whereas the steering mechanism operates to steer the camera dolly in the desired direction when the ground wheels are employed for the rolling motion, steering becomes unnecessary when the dolly moves on rails by means of the rail wheels, because the direction of movement of the dolly is then controlled by the rails themselves. Since with the known support wheel device the four steering shafts are coupled, e.g. by a chain drive which engages all four shafts in the same manner and degree whereby said coupling is such that all four steering shafts are caused always to turn through equal angles, it is impossible under this coupling constraint for the suspension to negotiate a non-straight rail configuration, because, e.g., in a curved section of rail adjoining a straight section, the rail wheels disposed on the curved section are forced into a different angle of rotation with respect to the longitudinal axis of the dolly than are the rail wheels disposed on the adjoining straight section. This constitutes a major drawback. Thus, the common steering of all four steering shafts, which is a necessary condition for easy steerability of the camera dolly when supported on the ground wheels, becomes a hindrance to guiding of the dolly on curved rails via the rail wheels.